Piezoelectric oscillator in the form of a tuning fork

ABSTRACT

A piezoelectric oscillator in the form of a tuning fork having two arms and being particularly useful as a time standard for timekeeping devices. The arms of the tuning fork which oscillate during operation of the device are decoupled or isolated from a carrier upon which the fork is mounted by two decoupling elements. The tuning fork is provided with electrodes carried by selected surfaces of the arms thereof in various symmetrical arrangements, including axial and central symmetry. One of the decoupling elements is disposed intermediate the arms of the tuning fork and the position at which the electrical connections are made to the electrodes so that the mass of the electrodes does not affect the oscillation of the arms. The piezoelectric oscillator is thus extremely frequency stable, efficient, and relatively uninfluenced by external factors.

United States Patent Ganter et al.

[ 1 Oct. 10,1972

[54] PIEZOELECTRIC OSCILLATOR IN THE FORM OF A TUNING FORK [73] Assignee: Gebrueder Junghans G.m.b.l-I.

Schramberg/Wuerttemberg, Germany [22] Filed: Feb. 12, 1971 [21] Appl. No.: 114,880

[30] Foreign Application Priority Data Feb. 27, 1970 0 Germany ..P 20 09 379.2

[52] US. Cl ..3l0/8.2, 58/23 TF, 84/457, 310/85, 310/94, 310/98 [51] Int. Cl. ..H0lv 7/00 [58] Field of Search ..310/8-83, 8.5, 3 10/91, 9.4, 9.6, 9.5, 9.7, 9.8; 58/23 TF;

[56] References Cited UNITED STATES PATENTS 3,425,310 2/1969 Grib et al ..84/457 2,806,400 9/1957 Grib ..58/23 TF 2,666,196 l/l954 Kinsley et al. ..3 10/81 X 3,131,320 4/1964 Shinada et al. ,.3 l0/9.6 3,128,397 4/1964 Shinada et al. ..3 10/95 FOREIGN PATENTS OR APPLICATIONS 1,539,922 9/1968 France ..3 10/82 Primary Examiner-.l. V. Truhe Assistant Examiner-B. A. Reynolds Att0rneyBums, Doane, Swecker & Mathis 5 7] ABSTRACT A piezoelectric oscillator in the form of a tuning fork having two arms and being particularly useful as a time standard for timekeeping devices. The arms of the tuning fork which oscillate during operation of the device are decoupled or isolated from a carrier upon which the fork is mounted by two decoupling elements. The tuning fork is provided with electrodes carried by selected surfaces of the arms thereof in various symmetrical arrangements, including axial and central symmetry. One of the decoupling elements is disposed intermediate the arms of the tuning fork and the position at which the electrical connections are made to the electrodes so that the mass of the electrodes does not affect the oscillation of the arms. The piezoelectric oscillator is thus extremely frequency stable, efficient, and relatively uninfluenced by external factors.

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PIEZOELECTRIC OSCILLATOR IN THEFORM OF A TUNING FORK BACKGROUND OF THE INVENTION specifically to a piezoelectric oscillator in the form of a lo tuning fork wherein theelectrodes for the stimulation and feed-back of oscillations are arranged on the prongs of the fork and wherein the fork is suspended or mounted on a mounting or a carrier plate which is mechanically decoupled from the tuning fork.

Piezoelectric oscillators in the form of tuning forks, e.g., quartz tuning forks, have advantages over quartz bars as time standards for timekeeping devices. For example, a quartz tuning fork-may be kept shorter than a quartz bar for the same frequency of oscillation. The suspension of the quartz tuning fork is less critical than that of the bar and the impulse strength is higher. Also, higher factors of quality with respect to frequency can be achieved.

The prior art timekeeping devices, quartz crystal tuning forks have been used astime standards. The stimulation of oscillation, has been accomplished by electrodes on only one prong of the fork and the detection or pick up of the oscillation has been accomplished by a second electrode system on the other prongof the fork. Mounting or suspension of the tuning fork has been accomplished by means of one -or more spiral springs which serve. simultaneously as a suspension means and a currentconductor. While such electrodes and suspension techniques have attained animproved degree of efficiency and frequency stability compared to other electrode arrangements and to fixedly mounting the tuning fork to a carrier plate, there is still much to be desired from both mechanical and frequency stability standpoints with respect to both the electrode arrangements and the mounting techniques, particularly where extremely small tuning forks are utilized, for example, in small wrist watches.

Generally, prior art tuning forks suffice where a large tuning fork suspendedfreely in space is required. However, where extremely small, firmly mounted tuning forks are necessary as in watches which are carried or worn and are therefore subject to shock, the frequency of oscillation of the tuning fork may be considerably affected by a number of external factors. For example, the type of mounting or suspension, the electrode arrangements, and the attachment of leads to the electrodes of the tuningfork may influence frequency and overall efficiency. Other frequency errors may result, for example, from dissymmetries of the prongs of the fork. As in the case of the influence on frequency caused by the mass of the attached supply and pick-up leads, such dissymmetries and the effect thereof on frequency increase with decreasing size and with the need for rapid mass production.

lt is therefore an object of the present invention to provide a novel piezoelectric oscillator having improved frequency stability and efficiency.

It is a further object of the present invention to provide a novel piezoelectric oscillator in the form of a tuning fork which isrelatively uninfluenced by shock impulses.

It is another object of the present invention to provide a novel suspension and electrode arrangement for a-piezoelectric oscillator in the form of a tuningfork.

According to the invention, these and other objects and advantages are accomplished by providing a piezoelectric oscillator in the'form of a tuning fork having two series connected decoupling elements disposed intermediate the arms of the tuning fork and a mounting or carrier plate. decoupling element is formed by recesses at the base of the tuning fork while a second decoupling element includes atleast one elastic connecting element between the base of the tuning fork and the carrier or mounting plate of the tuning fork. The spring constant of the second decoupling element, i.e., the elastic connecting element, is preferably kept considerably smaller than that of the first decoupling element. Specifically, the elastic connecting element is constructed and/or arranged in such a way that its spring constant is considerably less in the oscillating direction of the arms of the tuning fork than that of the first decoupling element. Moreover, the surface or area moment of inertia of the elastic connecting element is kept smaller preferably in a direction parallel-to the plane of oscillation of thearrns of the tuning fork than perpendicularly thereto. The elastic connecting element may also provide, for example, a power supply lead forthe electrode arrangement. a

The electrode arrangement is such that the electrical connections thereto are free of any crossings in route to or on the base of the tuning fork. Moreover, connection of external leads to the electrodes is accomplished on a base portion of the tuning fork which is mechanically decoupled from the armsof thetiming fork by the first decoupling element. The electrodes may be arranged only on the longitudinal surfaces of the arms or prongs of the tuning fork parallel to the plane of oscillation thereof or suitably distributed over all longitudinal sides of the arms of the tuning fork.

The electrodes are arranged in cross-section, symmetrically in various ways on the arms of the tuning fork. For example, the electrodes may be arranged axially symmetrically, i.e., symmetrically about the lonthe housing which is sealed in a gas-tight manner and which may then be substantially evacuated or filled with a suitable gas.

THE DRAWINGS The foregoing objects and advantages will become apparent to one skilled in the art to which the invention pertains from a perusal of the following detailed description when red in conjunction with the attached drawings in which:

FIGS. la and 1b are perspective front and rear views of one embodiment of a quartz tuning fork according to the invention;

More specifically, a first i FIG. 2 is a view in cross-section of the tuning fork of FIG. la taken along the lines lI-II;

FIG. 3 is a perspective view of another embodiment of a tuning fork according to the invention;

FIG. 4 is a perspective view of the tuning fork of FIG. 3 showing another embodiment of an elastic connecting element utilized therewith;

FIG. 5 is a view in cross-section of the tuning fork of FIG. 3 taken along the lines V-V;

FIGS. 6a and 6b are front and rear perspective views of another embodiment of a tuning fork in accordance with the present invention wherein the carrier for the tuning fork and the elastic connecting elements between the base of the tuning fork and the carrier have been omitted for the sake of clarity;

FIG. 7 is a view in cross-section of the tuning fork of FIG. 6a taken along the lines Vll- VII;

FIGS. 8a and 8b are front and rear perspective views of another embodiment of the tuning fork according to the invention with the omission of the carrier andthe elastic connecting elements as in FIGS. 6a and 6b;

FIG. 9 is a view in cross-section of the tuning fork of FIG. 8a taken along the line IX'IX; and

FIG. 10 is a perspective view of a tuning fork accord ing to the invention as assembled and mounted in a housing adapted to protect the assembly.

DETAILED DESCRIPTION In FIGS. 1a, lb and 2, a tuning fork generally designated 10 constructed of a suitable piezoelectric material, preferably quartz, is shown. The tuning fork 10 has two arms 11 and 12 and a base generally indicated at 13 which is subdivided into two parts 13a and 13c by two lateral recesses 13b and 13d. The lateral recesses 13b and 13d form a decoupling element generally indicated at 13c which essentially decouples the base portion 13a from the base portion 13a of the tuning fork thereby permitting the attachment of various power supply leads at the'base portion 13a without influencing the frequency of thetuning fork.

The base portion 13a is connected to a carrier or a mounting plate via an elastic connecting element 14, which, for example, may be T-shaped. The base portion 13a may be glued to the transverse element of the T-shaped elastic connecting element 14 and the other end of the connecting element 14 may be inserted into a slot in the carrier 15 and welded or soldered thereto. The connecting element 14 is preferably an electrically conductive material so that this connectingelement can simultaneously be used as a current carrying lead. For this purpose, a solder or other conductive junction 25 is provided between one electrode 24 and the connecting element 14 as illustrated in FIG. 1b. Since electrically conductive connections are utilized, the connecting element 14 is constructed of a weldable or solderable material and is preferably steel.

The connecting element 14 is preferably selected such that its spring constant in the direction of oscillation of the arms 11 and 12 of the tuning fork i.e., in the plane of oscillation of the tuning fork defined by a plane containing the longitudinal axes of the arms 11 and 12, is less than the spring constant in the direction perpendicular to the direction of oscillation of the arms 11 and 12. In this perpendicular direction, the connecting element 14 must protect the tuning fork 10 from breakage caused by outside impulse effects. In addilarge spring constant is selected in this perpendicular direction.

The transverse element of the T-shaped connecting element 14 may alternatively be soldered or otherwise connected to the base portion of the tuning fork 10. For example, a portion of the base portion 30c of the tuning fork may be metalized in a suitable conventional manner and the connecting element 14 soldered thereto.

With continued reference to FIGS. 1a, lb and 2, the electrodes 16-19 and 24 may be attached to the lateral longitudinal surfaces of the arms 11 and 12 of the tun-' ing fork'in parallel with the plane of oscillation of the tuning fork and symmetrically about a plane containing the longitudinal axis of the tuning fork and normal to the plane of oscillation. The attachment may be accomplished in any suitable conventional manner, for example, by steaming or other suitable, conventional processes. The electrodes 16-19 and 24 are arranged in this embodiment in axial symmetry. The electrodes 16 and 17 and the electrodes 18 and 19 are essentially U- shaped and lie in the same plane on the narrow sides, i.e., the front surfaces, of the arms 11 and 12 of the tuning fork. Conductive paths traversing the mechanical decoupling element 13c are provided between the electrodes 16-19 and 24 and the base portion 130 without any crossing of these paths. Connecting wires 20 and 21 are connected to portions of the conductive paths from the electrodes 16-19 located on the base portion 130 and, as previouslydescribed, the connecting element 14 is electrically connected to the electrode 24 on the base portion 13c to provide a path for current thereto.

'Additional masses 22 and 23 are attached at convenient, symmetrical occasions on the arms 11 and 12 of the tuning fork as illustrated in FIG. In. It is thus possible to trim away some or all of the masses 22 and 23 to make the arms 11 and 12 symmetrical or to provide fine adjustment of the frequency oscillation of the tuning fork.

Other electrode arrangements and/or suspensions or mounting techniques of the present invention are illustrated in FIGS. 4-9. The actual crystal tuning fork may be physically constructed essentially as described in connection with FIGS. 1a, lb and 2 and this physical construction will therefore not be described in connection with these further embodiments.

In the embodiment illustrated in FIGS. 3-5, electrodes 33-35 and 38-40 are provided on all longitudinal surfaces of the arms of the tuning fork, the surfaces of which are essentially equal in area. These electrodes are arranged symmetrically about the longitudinal axis of the tuning fork, i.e., axially symmetrically. As shown more clearly in FIG. 5, the electrodes 33 and 40 each pass around one edge of the respective arms of the tuning fork upon which they are mounted and actually form two electrodes. The electrodes 35 and 38 are provided with. a conductive path 350 running to the base portion 13c, the electrodes 33 and 40 are provided with a conductive path 33a running to a central location on the base portion 130 on one side thereof, and the electrodes 39 and 34 are provided with a conductive path 34a (not shown) running to a central location on the base portion 130 at the rear of the tuning fork. Power is supplied or signals picked up from the electrodes 33 and .40 by a supply lead 21 connected to the conductive portion 33a at a convenient location on the base portion 130. Likewise, power is supplied for signals picked up from the electrodes 34 and 39 by a supply lead 20 connected to the conductive path 34a at a convenient location on the base portion 130.

The tuning fork of FIG. 3 is mounted on the carrier by two elastic connecting elements 30 and 31 connected between the base portion 13c and'the carrier 15. Additionally, at least one of the connecting elements 31 provides a power supply lead which may be connected by way of a soldered junction 32 to the conductive path 35a connected to the electrodes 35 and 38.

In the embodiment of FIG. 4, a single elastic connecting element 41 is provided for mounting the tuning fork on a suitable carrier. The connecting element is inserted into a slot in the carrier and is also inserted into a slot 42 in the base portion 136' of the tuning fork. The connecting-element may be secured in the slots in any suitable manner and a soldered junction may be provided to establish a conductive path between selected ones of theelectrodes and the connecting element 41.

As shown in the embodiment of FIG. 3, by way of ex-' ample, additional masses 36 and 37 may be arranged laterally on the ends of the tuning fork to provide fine adjustments as previously described.

In FIGS. 6a, 6b and 7,,another embodiment of the present invention is illustrated. The electrodes on the armsof the tuning forks in thisembodiment are arranged in universal symmetry, i.e., both centrally, and axially symmetrically, and the surface areas of the individual electrodes arranged on the longitudinal surfaces of the arms of the tuning forks are of substantially equal area. Those electrodes which act together are connected together electrically by conductive paths provided at convenient locations on the tuning fork. For example, the electrodes 50 and 51 which are on-opposite sides of one arm of the tuning fork are connected together by a conductive path 50/51. In a similar manner, the electrodes 52 and 53 are electrically connected by conductive paths 52/53, the electrodes 54 and 55 are means of a conductive path 54/55, the electrodes 56 and 57 by means ofa conductive path 56/57, and the electrodes 56 and 51 by means of a conductive path 56/51.

While the elastic connecting element between the decoupled base portion of the tuning fork and the carrier, as well as the carrier itself, is not shown, mounting described.

Another embodiment of the present invention is illustrated in FIGS. 8a, 8b and 9. In this embodiment, the

' posite sides of the arms which are parallel to the direction of oscillation of the arms and are essentially U-shaped. The electrodes and 72 are electrically connected by a conductive path 70/72, the electrodes 70 and 73 are electrically connected by a conductive path 70/73 and the electrodes 71 and 73 are electrically connected by a conductive path 71/73. To prevent interruptions, i.e., breaks, in 'the conductive paths where these conductors bend around the arms of the tuning fork, the edges of the tuning fork arms may be broken or rounded in appropriate places as illustrated.

FIG. 10 shows a tuning fork, for example the tuning fork illustrated in FIG. 3, mounted ona base plate 81 for housing and final assembly. The carrier for mounting plate 15 of the tuning fork is connected to the base I plate 81 and the base plate 81 is provided with a glass stopper through which the supply lead 20 and 21 pass in a gas type manner. The base plate may be, for example, constructed of steel and, of course, it should be understood that any of the previously described tuning forks may be arranged on the base plate 81 in this manner.

After the electrical connections have been made to the tuning fork and the tuning fork has been precisely balanced, a cover 82 maybe placed over the tuning fork in contact with the base plate 81 and sealed in an air-tight manner. The housing formed by the cover 82 and the base plate 81 can then be either evacuated in a known manner or filled with a suitable gas.

It should also be noted that the tuning forks of FIGS. 3 and 4, for example, are additionally advantageous when sealed in this manner since the same evacuation mass can be used for both sides of the arms of the tuning forks. When finally assembled in this manner, the tuning fork according to the present invention may be utilized as a time standard for time keeping devices, particularly for small watches such as wrist watches which can be worn.

The present invention may thus be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The presently disclosed embodiments are therefore to be considered in all respects as illustrative and not restrictive, the scope of the invention being indicated by the appended claims rather than by the foregoing description, and all changes which come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.

What is claimed is: 1. Apparatus for providing a time standard for timekeeping devices comprising: a. piezoelectric oscillator in the form of a tuning fork having two elongated arms, said arms being adapted to oscillate in a plane of oscillation defined by a plane substantially containing the longitudinal axes of said arms,

at least one elastic connecting element intermediate and connected to said second base portion and said carrier,

said elastic connecting element defining a second decoupling element,

said first and second decoupling elements being disposed in series relationship between said first base portion and said carrier,

said first and second decoupling elements having predetermined spring constants,

the spring constant of said second decoupling element being less than the spring constant of said 7 first decoupling element in a direction defined by the plane of oscillation of the arms of the tuning fork.

2. Apparatus for providing a time standard for timekeeping devices comprising:

a piezoelectric oscillator in the form of a tuning fork having two elongated arms,

said arms being adapted to oscillate in a plane of oscillation defined by a plane substantially containing the longitudinal axes of said arms,

said tuning fork including a base divided by a plurality of peripheral, lateral recesses into connected first and second base portions,

the arms of said tuning fork being connected to said first base portion,

the connection between said first and second base portion defining a first decoupling element;

a plurality of electrodes carried by said tuning fork to stimulate and detect oscillation thereof;

a carrier for mounting said tuning fork in a timekeeping device; and,

at least one elastic connecting element intermediate and-connected to said second base portion and said carrier,

said elastic connecting element defining a second decoupling element,

said first and second decoupling elements being disposed in series relationship between said first base portion and said carrier,

the area moment of inertia of the second decoupling element in a direction defined by the plane of oscillation of the arms of the tuning fork being less than the area moment of inertial of the second decoupling element in a direction normal to the plane of oscillation.

3. Apparatus for providing a time standard for timekeeping devices comprising:

a piezoelectric oscillator in the form of a tuning fork having two elongated arms,

said arms being adapted to oscillate in a plane of oscillation defined by a plane substantially containing the longitudinal axes of said arms, said tuning fork including a base divided by a plural:-

said elastic connecting element defining a second decoupling element,

said first and second decoupling elements being disposed in series relationship between said first base portion and said carrier,

said second decoupling element being electrically conductive and being electrically connected to at least one of said electrodes. 

1. Apparatus for providing a time standard for timekeeping devices comprising: a piezoelectric oscillator in the form of a tuning fork having two elongated arms, said arms being adapted to oscillate in a plane of oscillation defined by a plane substantially containing the longitudinal axes of said arms, said tuning fork including a base divided by a plurality of peripheral, lateral recesses into connected first and second base portions, the arms of said tuning fork being connected to said first base portion, the connection between said first and second base portion defining a first decoupling element; a plurality of electrodes carried by said tuning fork to stimulate and detect oscillation thereof; a carrier for mounting said tuning fork in a timekeeping device; and, at least one elastic connecting element intermediate and connected to said second base portion and said carrier, said elastic connecting element defining a second decoupling element, said first and second decoupling elements being disposed in series relationship between said first base portion and said carrier, said first and second decoupling elements having predetermined spring constants, the spring constant of said second decoupling element being less than the spring constant of said first decoupling element in a direction defined by the plane of oscillation of the arms of the tuning fork.
 2. Apparatus for providing a time standard for timekeeping devices comprising: a piezoelectric oscillator in the form of a tuning fork having two elongated arms, said arms being adapted to oscillate in a plane of oscillation defined by a plane substantially containing the longitudinal axes of said arms, said tuning fork including a base divided by a plurality of peripheral, lateral recesses into connected first and second base portions, the arms of said tuning fork being connected to said first base portion, the connection between said first and second base portion defining a first decoupling element; a plurality of electrodes carried by said tuning fork to stimulate and detect oscillation thereof; a carrier for mounting said tuning fork in a timekeeping device; and, at least one elastic connecting element intermediate and connected to said second base portion and said carrier, said elastic connecting element defining a second decoupling element, said first and second decoupling elements being disposed in series relationship between said first base portion and said carrier, the area moment of inertia of the second decoupling element in a direction defined by the plane of oscillation of the arms of the tuning fork being less than the area moment of inertial of the second decoupling element in a direction normal to the plane of oscillation.
 3. Apparatus for providing a time standard for timekeeping devices comprising: a piezoelectric oscillator in the form of a tuning fork having two elongated arms, said arms being adapted to oscillate in a plane of oscillation defined by a plane substantially containing the longitudinal axes of said arms, said tuning fork including a base divided by a plurality of peripheral, lateral recesses into connected first and second base portions, the arms of said tuning fork being connected to said first base portion, the connection between said first and second base portion defining a first decoupling element; a plurality of electrodes carried by said tuning fork to stimulate and detect oscillation thereof; a carrier for mounting said tuning fork in a timekeeping device; and, at least one elastic connecting element intermediate and connected to said second base portion and said carrier, said elastic connecting element defining a second decoupling element, said first and second decoupling elements being disposed in series relationship between said first base portion and said carrier, said second decoupling element being electrically conductive and being electrically connected to at least one of said electrodes. 